Machines such as mining trucks, locomotives, marine vessels and the like have recently begun using alternative fuels, alone or in conjunction with traditional fuels, to power their engines. For example, large displacement engines may use a gaseous fuel, alone or in combination with a traditional fuel such as diesel, to operate. Because of their relatively low densities, gaseous fuels, for example, natural gas or petroleum gas, are carried onboard vehicles in liquid form. These liquids, the most common including liquefied natural gas (LNG) or liquefied petroleum gas (LPG), are stored in insulated tanks on the machine at cryogenic temperatures, from where a desired quantity of fuel is pressurized, evaporated, and provided to fuel the engine.
Pumps used to pressurize LNG or LPG for delivery to the engine of the machine may include a piston, that is reciprocally mounted in a cylinder bore. The piston is moved back and forth in the cylinder by hydraulic pressure to actuate a pumping assembly of the pump to draw in and then pressurize the LNG. Power to move the piston may be provided by different means, such as electrical, mechanical or hydraulic power. Pumps that include multiple pistons are also known.
An issue with cryogenic pumps in such engine systems is that extreme operating conditions may limit operating life span. In particular, a limiting factor with respect to the operating life span of such pumps is the seals in the pump. LNG typically has a relatively low lubricity. As a result, the pump seals that are exposed to the pressurized LNG can wear out relatively quickly due to lack of lubrication. These pump seals can be hard to replace. Lubricants typically freeze at the low temperatures at which the LNG is maintained, for example −160° C., making it difficult to add lubricant for the seals into the system.
U.S. Pat. No. 6,899,146 (“the '146 patent”) discloses an apparatus for dispensing LNG to natural gas powered motor vehicles. The apparatus includes a LNG flow path and a CNG flow path, each of which communicate with a LNG storage tank. LNG from the LNG flow path may be selectively directed to the CNG flow path which includes a vaporizer configured to produce CNG from the pressurized LNG. The '146 patent discloses that a source of lubricant can be coupled with the CNG flow path to introduce and mix lubricant with the CNG to provide lubrication of the components used to process and combust the CNG. However, the '146 patent discloses no system or method for introducing lubricant into the LNG path and thus no source of lubrication is provided for the components associated with handling the LNG.